In order to drive a screw or other fastener into a substrate, various driving tools, such as torque wrenches are utilized. Torque wrenches are utilized primarily because of their ability to closely control the amount of torque that can be applied to the fastener. Thus, the fastener can be driven into the substrate with the desired level of torque, thereby preventing damage from being done to the substrate as a result of overdriving the fastener into the substrate.
While this ability is important in many areas, it is especially important in the medical field, where fasteners are often utilized to hold parts of a patient's anatomy together. Therefore, to prevent damage from being done to the patient by the fastener, it is necessary to insert the fasteners into the patient with a precise amount of force to engage the fasteners with the patient without damaging the body portions of the patient to which the fasteners are affixed.
To accomplish this, a number of different torque limiting mechanisms have been developed for use with fastener-driving tools, such as torque wrenches, which allow the fastener-engaging portion of the wrench to slip with regard to the driving portion of the wrench when a preset maximum torque value has been exceeded. In this manner, the torque limiting mechanism enables the individual utilizing the tool to use the necessary force to engage the fastener with the substrate, but mechanically disengages the tool from the fastener when the individual applies too much torque to the fastener via the tool.
When using fastener-driving tools including torque limiting mechanisms of this type, many of these mechanisms do not provide any indication of the actual torque level at which the wrench or other tool is being utilized prior to the torque limiting mechanism being actuated. In other words, other than the initial setting for the limit at which the torque limiting mechanism is set to disengage the driving portion of the tool from the fastener engaging portion, there is no indication of this level or how close the tool is being operated to this level provided to the individual using the tool. As a result, oftentimes the individual utilizing the wrench exerts more torque through the tool to the fastener than is required, which causes the torque limiting mechanism to activate, when it was not necessary for the tool to be operated at that torque level.
Therefore, it is desirable to develop a tool including a torque limiting mechanism that also provides an indication of the amount of torque being applied by the tool prior to the actuation of the torque limiting mechanism, such that the proper or desired amount of torque below the limit at which the mechanism will operate can be applied to an item utilizing the tool.